The pyrocatecholic compound L-DOPA is useful in treating Parkinson's disease. Other pyrocatecholic compounds are useful in photography, dyeing processes, and as chemical reagents and pharmaceuticals.
It is known that monophenolic compounds can be converted into pyrocatecholic compounds via a reaction catalyzed by monophenol monooxygenase (EC 1.14.18.1) (also known as tyrosinase). Various methods for preparing these pyrocatecholic compounds use tyrosinases extracted from plants, animals (Evans, W. C., Biochem, J. 31, 2155 (1937)) and a variety of microorganisms (U.S. Pat. No. 3,671,397). These methods, however, result in low yields of pyrocatecholic compounds. The main reasons for this low yield can be explained by considering the following reaction pathway: ##STR1## Where: E=monophenol monooxygenase
MP=monophenolic compound PA1 PC=pyrocatecholic compound PA1 OAQ=orthoanthraquinone PA1 C.sub.rd =Reducing agent, reduced form PA1 C.sub.ox =Reducing agent, oxidized form
In the first reaction, monophenolic compounds are oxidized to form pyrocatecholic products under the catalytic action of monophenol monooxygenase. However, the pyrocatecholic products formed are further oxidized, under the action of oxygen and this same monooxygenase, into an orthoanthraquinone, which undergo a series of subsequent reactions to finally form melanin. The overall results are low yields of pyrocatecholic products and complex mixtures of unwanted products. Sophisticated separation procedures are needed to purify the desired products.
Conventional methods for minimizing further oxidation of pyrocatecholic products involve:
1. Using vitamin C or sulfite as reducing agent to reduce orthoanthraquinone back into pyrocatecholic compound (W. C. Evans, Biochem. J., 31: 2162-2170 (1937).
2. Adding a protecting group to an appropriate position on the starting monophenolic compound to lower the oxidation rate of the pyrocatecholic product by the steric hindrance. For example, when tyrosine is used as the starting monophenolic compound, formyl or acetyl groups are used to protect the tyrosine amino group (F. E. Semersky, U.S. Pat. No. 3,812,009 (1974).
Although these methods are helpful to the production of pyrocatecholic compounds, they are complex and costly. More efficient methods of manufacturing pyrocatecholic compounds are needed.